I suggest you ...

Words with more added contexts go first in reviewing flashcards

We know that words with higher frequency appear first when reviewing flashcards. But it would be more useful and intelligent to use the number of added contexts to a word and you review words that have more added contexts first. Because here is the thing. I read material on topics I'm interested in, and some vocabulary I see more often. And that vocabulary is essential to me more than the other, maybe with higher general frequency.

This is a great idea! It would also help with the 'beta' languages that don't actually have frequency ordering yet, users could basically enforce their own frequency ordering by adding the word in multiple contexts.